The goal of this research is to identify specific central nervous system processes that are altered by psychotropic drug treatment during symptom improvement. Behavioral, neuropsychologic, central neurophysiologic, and neurochemical measures will be obtained in individuals with a diagnosis of endogenous depression, schizophrenia, hypomania, and healthy controls who will be invited to participate in the study prior to, during, and following drug administration. Detailed self-reports, observational ratings, neuropsychologic testing, clinical neurophysiologic measures, and urine and cerebral spinal fluid measures of neurochemical variables will be obtained prior to, during and following drug administration. Of particular interest are the relationships between symptom change and the measured variables in different drug treatments and whether pre-treatment measures relate to symptom response during drug administration. The information obtained from their study will be used to design and guide more detailed neurocellular and neurochemical studies in homologous animal models with the eventual goal of elucidating the clinically operant neuropharmacologic mechanisms. Behavioral measure, intra-cerebral electrical recordings and neurochemical measures will be obtained from animals in order to more thoroughly investigate mechanisms of drug action at the chemical, physiologic, and behavioral levels.